1. Field of the Invention
The present invention relates to an image forming apparatus which forms an image on a sheet.
2. Description of the Related Art
In the related art, image forming apparatuses, such as a copying machine, a printer and a facsimile machine, are each provided with an image forming portion and a sheet conveying apparatus for conveying a sheet to the image forming portion by means of conveying rollers. Further, the sheet conveying apparatus may include an abutment member, which is provided in a sheet conveying path, and applied with a force in a direction opposite to a sheet conveying direction, and also moves from a position of being pressed by a sheet being conveyed to abut the sheet against the applied force to a position of allowing passage of the sheet while being in contact with the sheet.
Incidentally, in the conventional image forming apparatus, when a conveying roller is formed in taper shape or alignment of the conveying rollers is displaced, or in some other case, a sheet may be skew-fed during conveyance of the sheet. Especially when a sheet is fed from a cassette or a plurality of sheets is separated so as not to be simultaneously conveyed, skew feeding tends to occur since a roller width is small and the sheet cannot be sufficiently held for rotation. When the sheet is skew-fed as thus described, the accuracy in image forming position deteriorates.
Thereat, in the conventional image forming apparatus, a skew correcting portion is provided in the sheet conveying apparatus, and the accuracy in image forming position is sought to be improved by correcting skew feeding of the sheet in this skew correction portion. As such a skew correcting portion, for example, there is one provided with a shutter applied with a force by a spring or the like in a direction opposite to the sheet conveying direction, and makes this shutter abut the tip end of a sheet (see U.S. Pat. No. 6,011,948).
In the skew correcting portion using such a shutter, in the case of correcting skew feeding of a sheet, the sheet being skew-fed is first abutted by the shutter. Herein, when the sheet is being skew-fed, one of both ends of the sheet being skew-fed abuts the shutter. At this time, since the shutter being applied with a force by the spring or the like cannot move, the sheet in the end abuts the shutter as the entire tip end thereof follows a generating line of the shutter. Following the generating line of the shutter as thus described can correct skew feeding of the sheet.
Further, when the tip end of the sheet follows the generating line of the shutter as thus described, the shutter can then be rotated against the spring or the like applying the force to the shutter due to the stiffness of the sheet, so that the sheet can pass while rotating the shutter. In addition, for obtaining a favorable output image, it is important to correct skew feeding of a sheet before an image is transferred to the sheet in the image forming portion. Further, a position where the correction is made is more favorably closer to the image forming portion. Incidentally, in such conventional sheet conveying apparatus and image forming apparatus provided with this sheet conveying apparatus, when a sheet passes while rotating the shutter, the shutter comes to press the sheet surface. Herein, the stronger the applied force that is applied to the shutter, the more the skew correcting ability improves, but when the applied force is thus made stronger, a pressing force that is applied to the sheet by the shutter increases.
Then, when the pressing force that is thus applied to the sheet increases, the surface of the sheet may be damaged. Especially, glossy paper or the like with a coated surface, which is used with the recent colorization, tends to be damaged on the surface, and a damage that occurs during passage through the shutter appears when a toner image is formed. Further, depending on a type of sheet, charging may occur due to friction that occurs during passage through the shutter, thereby to prevent accurate formation of a toner image. As thus described, although increasing the applied force that is applied to the shutter improves the skew correcting ability, it may cause deterioration in quality of an image formed on the sheet.
It should be noted that, other than the shutter, the conventional sheet conveying apparatus is provided with a conveying path switching member which switches the sheet conveying path as the abutment member that moves from a position of being pressed by a sheet being conveyed to abut the sheet to a position of allowing passage of the sheet while being in contact with the sheet surface. Also at the time of passage through such a conveying path switching member, although increasing an applied force of the conveying path switching member can reliably switch the sheet conveying path, the sheet may be damaged at the time of passage thereof, to cause deterioration in quality of an image formed on the sheet.